A color liquid crystal display device widely used in recent years among color display devices users has several hundred thousands to several million pixels. Each pixel is composed of R (red), G (green) and B (blue) sub-pixels. In order to display the R, G and B for each sub-pixel, R, G and B color filters are used in many cases, and a full color image is obtained by combining displays of the sub-pixels using these color filters. In the case of using such color filters, two-thirds of a light is absorbed by these color filters, and theoretically, approximately one-third of the light is only usable. In this connection, a color filterless display device performing color display without using the color filters is under study.
The following documents are considered herein:
[Patent Document 1] Gazette of Japanese Patent Laid-Open No. 2000-241812 (pp. 3 to 4, FIG. 1)
[Patent Document 2] Gazette of Japanese Patent Laid-Open No. Hei 9 (1997)-311329 (p. 6, FIG. 1)
[Patent Document 3] Specification of US Patent Application Publication No. 2002-0075427
FIG. 13 is a view showing an example of a color filterless liquid crystal display device, a configuration of a conventional color filterless and direct view liquid crystal display device using a spectral element (for example, refer to Patent Document 1). The device shown in FIG. 13 includes a light source 401 using, for example, a white fluorescent tube, an incidence optical system 402, a reflection sheet 403, a wedge-shaped light guide plate 404, a diffraction grating 405, and a cylindrical lens sheet 406 that is an optical element including a plurality of cylindrical lenses. Moreover, the device includes polarization films 407 sandwiching a liquid crystal cell 408 there-between, a liquid crystal layer 410 sandwiched between glass 409 and glass 409, all three of which compose the liquid crystal cell 408, and a diffusion/viewing angle correction film 411 made of a light diffusion film, a transmission diffraction grating film or the like.
In this color filterless and direct view liquid crystal display device, a white light incident from the light source 401 is guided by the wedge-shaped light guide plate 404, and a planer light is emitted in the vicinity of a desired incident angle. The white light incident from the wedge-shaped light guide plate 404 is separated by an optical element (spectral element) such as the diffraction grating 405 (and an optical hologram). By this light separation, three-color diffracted light of the R, G and B is emitted at angles where the blue (B) light and the red (R) light are arrayed to be substantially symmetric bilaterally with respect to the green (G) light diffracted to a frontal direction as a center. The diffracted light of the respective colors is made incident onto the cylindrical lens sheet 406. Here, one pixel among the display pixels is composed of three sub-pixels of the R, G and B. With regard to the light incident onto the cylindrical lens sheet 406, for the liquid crystal cell 408, the R light is made incident onto a sub-pixel for the R, the G light is made incident onto a sub-pixel for the G, and the B light is made incident onto a sub-pixel for the B. Then, transmission and cutoff of the light is controlled for each sub-pixel. On a surface of the liquid crystal cell 408, an emitted light from the liquid crystal cell has emission angles different depending on the wavelengths due to diffraction angles depending on wavelengths of the colors. Accordingly, in order to widen a viewing angle of the liquid crystal cell 408, the light diffusion/viewing angle correction by the diffusion/viewing angle correction film 411 is performed. Note that, also in other color display devices such as a color filterless liquid crystal projection device, lights of the respective colors, which is made incident onto a liquid crystal cell in a state of being emitted from a white light source, separated by a dichroic mirror, a diffraction grating or the like, and condensed by a lens element, has different incident angle for each of the respective colors of the R, G and B.
However, in the conventional color filterless and direct view liquid crystal display device as shown in FIG. 13, a problem remains in terms of an effect of such a viewing angle correcting function member. By use only of the usual diffusion/viewing angle correction film 411, the emission angles from the liquid crystal cell, which depend on the wavelengths, are maintained even after the emitted light transmits through the diffusion/viewing angle correction film 411. In order to equalize color reproductivity and color balance and to widely secure the viewing angle, it is desired to add a far more improvement. Accordingly, it is also conceivable to separately use a transmission diffraction grating film as the viewing angle correcting function member. However, film design to control diffraction efficiencies different depending on the wavelengths and to correct intensity of the incident light of every wavelength with high accuracy into a distribution of the equalized viewing angles is accompanied with difficulty. Moreover, a significant lowering of a peak value of luminance to the frontal direction cannot be avoided. For example, a relative value of luminance of the emitted light on the front in comparison to the incident light onto the correction film is undesirably lowered to 30 to 40%. Furthermore, because of a combination of the materials having the different refractive indices, fabrication itself of a film into a shape combining high diffraction efficiency and a smooth surface is difficult. For example, in a diffraction grating having a triangular cross-sectional shape and using materials with refractive indices of 1.42 and 1.57, arithmetically, such a shape incapable of being fabricated, as in which an inner inclination angle between the two layers is 70 to 80 degrees, is needed.
FIGS. 14(a) and 14(b) are graphs showing distributions of the emitted light in the color filterless and direct view liquid crystal display device. FIG. 14(a) shows a distribution of the emitted light in the case where the viewing angle correcting diffraction grating is not provided, and FIG. 14(b) shows a distribution of the emitted light in the case where the transmission diffraction grating film is concurrently used as the viewing angle correcting function member. In each of the graphs, an abscissa axis represents an output angle, an ordinate axis represents transmissivity, and the distributions of the emitted light of the respective colors R, G and B are shown. In comparison with the case where the viewing angle correcting diffraction grating is not provided, which is shown in FIG. 14(a), in the case where the viewing angle correcting diffraction grating is provided, which is shown in FIG. 14(b), each center of the emitted light R, G and B comes close to a frontal direction of a panel. However, deviations among the lights of the respective colors are not removed, and the viewing angle correcting function member does not necessarily have a sufficient viewing angle correcting function.
The following should be noted. It has been measured that the color reproductivity (an area of a region displayable by the color display device in a chromaticity diagram) in the frontal direction in the case of concurrently using the transmission diffraction grating film as the viewing angle correcting function member becomes, for example, approximately 38% at the NTSC rate, which remains equal to or less than 42% at the NTSC rate of a direct view liquid crystal display device added with an existing 13.3-inch color filter. Moreover, if a condition of a viewing angle at which chromaticity is regarded as uniform is defined such that an error between a subject emitted component and an emitted component to the frontal direction falls within a range equal to or less than 0.02 in both chromaticity coordinates x and y, it has been confirmed that an emission angle range meeting the condition remains within, for example, a narrow range from −5 to +7 degrees. Because of these defects, with the transmission diffraction film, it is difficult to accomplish a sufficient viewing angle correcting function in luminance/chromaticity. Accordingly, a new viewing angle correcting method for improving viewing angle performance is required. Moreover, with regard to the luminance, from an observation of the inventors of the present invention, it is grasped that, for example, a luminance value on the front side before adding the transmission diffraction grating film is approximately 217 cd/m.sup.2, and a luminance value on the front side thereafter is approximately 85 cd/m.sup.2, both of which are results of attenuation to 40% or less in such an insufficient state of the color reproductivity. Therefore, an improvement for enhancing the luminance is also necessary.
Here, as the conventional viewing angle correcting function member, a structure has been proposed, in which lens-shaped or prism-shaped concave portions are processed and formed in a size corresponding to opening portions of the respective sub-pixels of the R, G and B on a black matrix-side surface of an emission-side glass substrate of the liquid crystal cell, and polymer having a refractive index higher than that of the glass substrate is injected into the concave portions, thus planarizing the surface (for example, refer to Patent Document 2). Moreover, the inventors of the present invention have proposed a technology in which a simple prism structure or a Fresnel-type microprism structure is introduced to the color filterless and direct view liquid crystal display device (refer to Patent Document 3).
In the above-described technology described in Patent Document 2, a viewing angle correction effect to the frontal direction by refraction can be expected to some extent. However, a cycle of a lens/prism structure is designed while corresponding to an amount of one pixel, that is, of three sub-pixels, and accordingly, in terms of paralleling the emitted light by restricting an angle expansion phenomenon itself thereof, which is caused by the condensing function element between a backlight and the liquid crystal cell, a diffusion suppression effect cannot be expected. Particularly, though an R light and a B light, which are made incident onto ends of a lens portion (denoted by a reference numeral 30 in FIG. 1), are illustrated as if both of the light became parallel to each other when being emitted in the content illustrated in FIG. 1 of Patent Document 2, the incident light is actually emitted to a diffusing direction on such illustrated ends of the lens portion. Therefore, a sufficient angle correction cannot be performed.
Moreover, in the technology proposed in Patent Document 3, far more problems to be solved for practical use are left. For example, a light travels from a low refractive layer to a high refractive layer in the technology proposed in Patent Document 3, and in order to perform the angle correction, it is necessary to improve a prism structure described in Patent Document 3. Particularly, it is necessary to study more in order to make it difficult to produce “shading” for the incident light.